I would like to comment that there appears to be a number of different causes for this error. In my case I had to reinstall the MVC3 RTM on the build machine (which has been building MVC3 projects for some time now).
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Mike CheelJun 11 '12 at 16:35

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Similar to the previous comment, I'm running VS2008 and suddenly I wasn't able to open a project that I've been working on for quite some time now. Finally reinstalled MVC2 and now it can open the project again.
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SanjamalOct 30 '12 at 19:16

@MikeCheel - Thank you so much for the tip, sir. I suspect that in my case I installed MVC 3 before I installed VS 2010, in which case I had to install MVC 3 again (I did not have to un-install first). When I went to install MVC 3, the dialog clearly indicated that it would be installing MVC 3 for VS 2010.
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Allan HorwitzOct 6 '13 at 12:32

14 Answers
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edit please see the answer further down, which is about 18 months newer, and actually solves the problem. This historically once-accurate answer is no longer as accurate. Leaving intact after the break for this reason. - thanks - jcolebrand

What edition of VS do you use? VS2008 Express, Standard, Pro or Team System? VS2010 Professional, Premium or Ultimate? I would expect that the project you downloaded was created using a higher edition of Visual Studio and uses some of those advanced features. Thus you can not open it.

EDIT: It is also possible that you lack some advanced frameworks like newer versions of Windows Mobile SDK, but if I recall correctly,the error message in such case is different.

Well, this makes first assumption much less probable as this is one of the highest editions. I agree that providing link to the project might be the greatest help. Also you could open .sln file with a notepad and check first line: what is Format Version there? I mean the project might be created with VS 2010.
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SergGrMay 3 '10 at 8:46

I'm getting this same error but using the latest version of Visual Studio 2010. Another machine with the same setup seems to be able to open the projects just fine. Only thing I can think of is that recently I uninstalled Visual Studio 2005. Running devenv /setup and such hasn't seemed to help at all so far.
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jpiersonAug 12 '10 at 23:46

Open up the .csproj file for your solution in wordpad or some text editor. Look for the ProjectTypeGuids. They indicate the required supported types for your solutions. Search the internet these GUIDs to find out what they require. For example E53F8FEA-EAE0-44A6-8774-FFD645390401 means it requires "MVC 3.0"

+1 - Missing MVC 3.0 was my issue, so thanks for this post! I may be too near-sighted, but you would think Visual Studio should be able to determine from the GUIDs what you are missing automatically rather than give you a boilerplate error message.
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JOpuckmanMay 29 '12 at 20:43

Instead of searching fr the GUIDs, you can simply delete the GUIds tags. Then try opening the project again. The second time opening you should get a more reasonable error message.

For instance my issue was that I did not install SharePoint Developer Tools when I installed Visual Studio 2010 on my development Virtual Machine. So when I tried opennign the project after deleting the GUIDs, VS2010 told me the path it was looking for did not exist.

Therefore VS2010 was looking for a SharePoint library that was not installed. I simply had to run the install again, and then add that feature.

+1 Thanks, that was it for me. Simply removed the entire <ProjectTypeGuids>{E3E379DF-F4C6-4180-9B81-6769533ABE47};{349c5851-65df-11da-938‌​4-00065b846f21};{fae04ec0-301f-11d3-bf4b-00c04f79efbc}</ProjectTypeGuids> node altogether. Those 3 GUIDs meant that it is a C# Web MVC 4.0 Application, and it was able to work that out without the node.
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Ralph LavelleOct 23 '13 at 6:21

If you are using VS 2010 and it is a ASP.NET project make sure you have the Visual Developer installed from the VS 2010 CD. This is not the free one, but part of what is required to work on ASP.NET projects in Visual Studio.

they will point on component you are missing. In my case it was ASP.NET MVC 2. Some guys get it worked by installing MVC 2 destribution.

My case was worse, because installation didn't work, but it turned out that it was because I had Express 2008 and 2010. I fixed it by uninstalling both 2008 & 2010 and installing only 2010 versions. For c# you need both Visual C# Express and Visual Web Developer express

As a addition to this, 'the project type is not supported by this installation' can occur if you're trying to open a project on a computer which does not contain the framework version that is targeted.

In my case I was trying to open a class library which was created on a machine with VS2012 and had defaulted the targeted framework to 4.5.
Since I knew this library wasn't using any 4.5 bits, I resolved the issue by editing the .csproj file from <TargetFrameworkVersion>v4.5</TargetFrameworkVersion> to <TargetFrameworkVersion>v4.0</TargetFrameworkVersion> (or whatever is appropriate for your project) and the library opened.

I was having this problem trying to add a WPF project in a WCF solution in Visual Studio Express 2012 for Web.
Deleting the content between the "ProjectTypeGuids" tags and leaving only the tags solved the problem. To know how to edit the .csproj file, read MindStalker comment.

Problem for me was my ProjectTypeGuid was MVC4 but I didn't have that installed on the target server. The solution was to change the ProjectTypeGuids to that of a Class Library, and include the MVC DLLs with the project rather than the project pick them up from the GAC.